1. Field of the Invention
This invention relates to an apparatus for displaying a fluorescence image, wherein a fluorescence image in accordance with characteristics of fluorescence, which is produced from a measuring site in a living body when the measuring site is exposed to excitation light, is displayed.
2. Description of the Related Art
There have heretofore been proposed apparatuses for displaying a fluorescence image by utilizing characteristics such that, in cases where excitation light having wavelengths falling within an excitation wavelength range for an intrinsic dye in a living body is irradiated to the living body, an intensity of fluorescence produced by the intrinsic dye in the living body varies for normal tissues and diseased tissues. With the proposed apparatuses for displaying a fluorescence image, excitation light having predetermined wavelengths is irradiated to a region of interest in a living body, the fluorescence produced by an intrinsic dye in the living body is detected, and the location and the infiltration range of diseased tissues are displayed as an image.
FIG. 10 shows typical fluorescence spectra of the fluorescence produced from normal tissues and the fluorescence produced from diseased tissues, which fluorescence spectra have been measured by the inventors. It is assumed that the thus produced fluorescence results from superposition of the fluorescence produced by various kinds of intrinsic dyes in the living body, such as FAD, collagen, fibronectin, and porphyrin. Ordinarily, when excitation light is irradiated to a region of interest in a living body, the fluorescence having a high intensity is produced by normal tissues, and the fluorescence having a low intensity is produced by diseased tissues. Therefore, in cases where information in accordance with the fluorescence intensity is displayed, a person who sees the displayed information is capable of recognizing the state of the diseased tissues. In many cases, the apparatuses for displaying a fluorescence image take on the form built in endoscopes, which are inserted into the body cavities, colposcopes, operating microscopes, or the like.
However, the aforesaid apparatuses for displaying a fluorescence image have the problems described below. Specifically, in cases where a region in a living body has protrusions and recesses, the distance between an excitation light irradiating system and the measuring site in the living body is not uniform. Therefore, it often occurs that the irradiance of the excitation light at the living body portion, which is exposed to the excitation light, is not uniform. The intensity of fluorescence is approximately in proportion to the irradiance of the excitation light, and the irradiance of the excitation light at the portion, which is exposed to the excitation light, is in inverse proportion to the square of the distance between the excitation light irradiating system and the portion, which is exposed to the excitation light. Accordingly, the problems occur in that diseased tissues, which are located close to the light source, produce the fluorescence having a higher intensity than the intensity of the fluorescence produced by normal tissues, which are located remote from the light source. The problems also occur in that the intensity of the fluorescence from normal tissues, which are located at a position inclined with respect to the excitation light, becomes low.
In order for the adverse effects of differences in measuring conditions, such as a measuring distance and a measuring angle, to be eliminated, there has been proposed an apparatus for displaying a fluorescence image by utilizing the characteristics such that a pattern of a fluorescence spectrum varies for the fluorescence produced from the normal tissues and the fluorescence produced from the diseased tissues. With the proposed apparatus for displaying a fluorescence image, as illustrated in FIG. 11, a quotient of division R/G is calculated from light intensity R of a red wavelength region and light intensity G of a green wavelength region. Also, information in accordance with the results of the division R/G is displayed on a monitor. In this manner, the location and the infiltration range of the diseased tissues are displayed as an image.
With the proposed apparatus for displaying a fluorescence image, the term of the fluorescence intensity depending upon the distance between the excitation light source and the region of interest in the living body and the distance between the region of interest in the living body and the fluorescence receiving means is canceled by the division R/G. Therefore, the term of the fluorescence intensity depending upon the distance between the excitation light source and the region of interest in the living body and the distance between the region of interest in the living body and the fluorescence receiving means can be ignored. However, the light intensity of the intrinsic fluorescence components of the green region in the intrinsic fluorescence produced from the diseased tissues is low. As a result, it often occurs that division by a value of zero occurs, and the operation becomes unstable.
An apparatus for displaying a fluorescence image as illustrated in FIG. 12 has been proposed in, for example, Japanese Unexamined Patent Publication No. 9(1997)-327433. With the proposed apparatus for displaying a fluorescence image, excitation light L9 is produced by an excitation light source 401 and is irradiated to a measuring site 60. Fluorescence L10, which is produced from the measuring site 60 when the measuring site 60 is exposed to the excitation light L9, is acquired via an endoscope 402. Fluorescence components of a red wavelength region and fluorescence components of a green wavelength region are selected from the fluorescence L10 by use of mirrors 403, 404 and filters 405, 406. The fluorescence components of the red wavelength region and the fluorescence components of the green wavelength region are detected respectively by high-sensitivity charge coupled device (CCD) image sensors 407 and 408. An image signal representing the fluorescence components of the red wavelength region, which image signal has been obtained from the CCD image sensor 408, is fed into an R signal input terminal of a color monitor 409. Also, an image signal representing the fluorescence components of the green wavelength region, which image signal has been obtained from the CCD image sensor 407, is fed into a G signal input terminal and a B signal input terminal of the color monitor 409. In this manner, relative intensities of the image signal representing the fluorescence components of the red wavelength region and the image signal representing the fluorescence components of the green wavelength region are displayed as a change in color on the color monitor 409.
With the apparatus for displaying a fluorescence image proposed in Japanese Unexamined Patent Publication No. 9(1997)-327433, there is no risk that division by a value of zero will occur. Also, the display color on the monitor changes in accordance with a ratio between the light intensity of the red wavelength region and the light intensity of the green wavelength region. Therefore, the person who sees the image displayed on the monitor is capable of recognizing the state of the diseased tissues in accordance with the display color.
However, the fluorescence, which is produced from the living body tissues when the living body tissues are exposed to the excitation light, is weak. With the apparatus for displaying a fluorescence image proposed in Japanese Unexamined Patent Publication No. 9(1997)-327433, only the light intensity of the red wavelength region and the light intensity of the green wavelength region are detected from the weak fluorescence, and a fluorescence image is formed. Therefore, the apparatus for displaying a fluorescence image proposed in Japanese Unexamined Patent Publication No. 9(1997)-327433 has the problems in that the efficiency, with which the fluorescence is utilized, cannot be kept high, adverse effects of photon noise, and the like, are apt to occur during photoelectric conversion for the detection of the light intensities, and a signal-to-noise ratio of the fluorescence image cannot be kept high.
The primary object of the present invention is to provide an apparatus for displaying a fluorescence image, wherein image information in accordance with fluorescence, which is produced from living body tissues when the living body tissues are exposed to excitation light, is acquired and displayed, such that an efficiency, with which the fluorescence is utilized, is enhanced, and a signal-to-noise ratio of a displayed fluorescence image is kept high.
Another object of the present invention is to provide an apparatus for displaying a fluorescence image, wherein a fluorescence image is displayed such that recognition as to whether fluorescence, which has been produced from a measuring site, is the fluorescence produced from normal tissues or the fluorescence produced from diseased tissues is capable of being made with a high reliability.
The present invention provides a first apparatus for displaying a fluorescence image, comprising:
i) excitation light irradiating means for irradiating excitation light to a region of interest in a living body, the excitation light causing the region of interest to produce intrinsic fluorescence, and
ii) image displaying means for acquiring image information in accordance with the intrinsic fluorescence, which is produced from the region of interest when the region of interest is exposed to the excitation light, and displaying the acquired image information,
wherein the image displaying means comprises:
a) light intensity detecting means for an entire measurement wavelength region, which light intensity detecting means detects a light intensity of intrinsic fluorescence components of the intrinsic fluorescence, which intrinsic fluorescence components have wavelengths falling within the entire measurement wavelength region,
b) light intensity detecting means for a partial measurement wavelength region, which light intensity detecting means detects a light intensity of intrinsic fluorescence components of the intrinsic fluorescence, which intrinsic fluorescence components have wavelengths falling within either one of a comparatively short wavelength region and a comparatively long wavelength region, and
c) display means for displaying a display color in accordance with a ratio between the light intensity, which has been detected by the light intensity detecting means for the entire measurement wavelength region, and the light intensity, which has been detected by the light intensity detecting means for the partial measurement wavelength region, the display color being displayed by the utilization of an additive color mixture process.
In the first apparatus for displaying a fluorescence image in accordance with the present invention, the light intensity detecting means for the entire measurement wavelength region should preferably detect a light intensity of intrinsic fluorescence components of the intrinsic fluorescence, which intrinsic fluorescence components have wavelengths falling within an entire visible wavelength region excluding the vicinity of the wavelength region of the excitation light.
The present invention also provides a second apparatus for displaying a fluorescence image, comprising:
i) excitation light irradiating means for irradiating excitation light to a region of interest in a living body, the excitation light causing the region of interest to produce intrinsic fluorescence, and
ii) image displaying means for acquiring image information in accordance with the intrinsic fluorescence, which is produced from the region of interest when the region of interest is exposed to the excitation light, and displaying the acquired image information,
wherein the image displaying means comprises:
a) light intensity detecting means for a red region, which light intensity detecting means detects a light intensity of intrinsic fluorescence components of the intrinsic fluorescence, which intrinsic fluorescence components have wavelengths falling within the red wavelength region,
b) light intensity detecting means for a green region, which light intensity detecting means detects a light intensity of intrinsic fluorescence components of the intrinsic fluorescence, which intrinsic fluorescence components have wavelengths falling within the green wavelength region,
c) light intensity detecting means for a blue region, which light intensity detecting means detects a light intensity of intrinsic fluorescence components of the intrinsic fluorescence, which intrinsic fluorescence components have wavelengths falling within the blue wavelength region, and
d) display means for displaying a display color in accordance with a ratio among the light intensity, which has been detected by the light intensity detecting means for the red region, the light intensity, which has been detected by the light intensity detecting means for the green region, and the light intensity, which has been detected by the light intensity detecting means for the blue region, the display color being displayed by the utilization of an additive color mixture process.
In the second apparatus for displaying a fluorescence image in accordance with the present invention, a sum of the light intensity, which has been detected by the light intensity detecting means for the red region, the light intensity, which has been detected by the light intensity detecting means for the green region, and the light intensity, which has been detected by the light intensity detecting means for the blue region, should preferably be the light intensity of intrinsic fluorescence components of the intrinsic fluorescence, which intrinsic fluorescence components have wavelengths falling within an entire fluorescence wavelength region excluding the wavelength region of the excitation light.
The first and second apparatuses for displaying a fluorescence image in accordance with the present invention should preferably be modified such that the display means is provided with a matrix operation circuit for transforming each of the light intensities into color signals and is constituted such that a color corresponding to each of the light intensities is capable of being selected arbitrarily by appropriately setting coefficients of an operation formula in the matrix operation circuit.
The detection of the light intensity of the intrinsic fluorescence components of the intrinsic fluorescence, which intrinsic fluorescence components have wavelengths falling within each wavelength region, by each of the light intensity detecting means may be performed with one of various techniques. For example, the intrinsic fluorescence having been produced from the measuring site may be separated by optical filters, or the like, into groups of the intrinsic fluorescence components having wavelengths falling within desired wavelength regions, which are to be employed ultimately, and the light intensities of the thus separated groups of the intrinsic fluorescence components may be detected respectively. Alternatively, the light intensity of intrinsic fluorescence components having wavelengths falling within a predetermined wavelength region, which is different in part from the desired wavelength region to be employed ultimately, may be detected, and the light intensity of the intrinsic fluorescence components having wavelengths falling within the desired wavelength region to be employed ultimately may be calculated from the detected light intensity with operation processing, such as adding and subtracting operations.
With the first apparatus for displaying a fluorescence image in accordance with the present invention, the light intensity of the intrinsic fluorescence components, which have wavelengths falling within the entire measurement wavelength region, and the light intensity of the intrinsic fluorescence components, which have wavelengths falling within either one of the comparatively short wavelength region and the comparatively long wavelength region, are detected. Also, the display color in accordance with the ratio between the two light intensities is displayed by the utilization of the additive color mixture process. In this manner, the light intensity of the intrinsic fluorescence components of the intrinsic fluorescence having been produced from the measuring site, which intrinsic fluorescence components have wavelengths falling within the entire measurement wavelength region, is capable of being utilized. Therefore, the efficiency, with which the intrinsic fluorescence is utilized, is capable of being enhanced, and the signal-to-noise ratio of the displayed fluorescence image is capable of being kept high.
Also, with the first apparatus for displaying a fluorescence image in accordance with the present invention, wherein the entire measurement wavelength region is the entire visible wavelength region excluding the vicinity of the wavelength region of the excitation light, the detection of the light intensity is not obstructed by the excitation light, and the intrinsic fluorescence having been produced from the measuring site is capable of being utilized efficiently.
With the second apparatus for displaying a fluorescence image in accordance with the present invention, the display color in accordance with the ratio among the light intensity of the intrinsic fluorescence components of the intrinsic fluorescence having been produced from the measuring site in the living body exposed to the excitation light, which intrinsic fluorescence components have wavelengths falling within the red wavelength region, the light intensity of the intrinsic fluorescence components, which have wavelengths falling within the green wavelength region, and the light intensity of the intrinsic fluorescence components, which have wavelengths falling within the blue wavelength region, is displayed by the utilization of the additive color mixture process. Therefore, the efficiency, with which the intrinsic fluorescence having been produced from the measuring site is utilized, is capable of being enhanced. Accordingly, the signal-to-noise ratio of the displayed fluorescence image is capable of being kept high. Also, a fine difference in light intensity between wavelength regions of the intrinsic fluorescence having been produced from the measuring site is capable of being displayed as a difference in tint.
Further, imaging means for detecting the fluorescence image is capable of being utilized also as the imaging means for an ordinary image. Therefore, the production cost of the apparatus for displaying a fluorescence image is capable of being kept low.
With the second apparatus for displaying a fluorescence image in accordance with the present invention, the sum of the light intensity of the intrinsic fluorescence components, which have wavelengths falling within the red wavelength region, the light intensity of the intrinsic fluorescence components, which have wavelengths falling within the green wavelength region, and the light intensity of the intrinsic fluorescence components, which have wavelengths falling within the blue wavelength region, may be the light intensity of the intrinsic fluorescence components, which have wavelengths falling within the entire fluorescence wavelength region excluding the wavelength region of the excitation light. In such cases, the detection of the light intensity is not obstructed by the excitation light, and the intrinsic fluorescence having been produced from the measuring site is capable of being utilized efficiently.
With the first and second apparatuses for displaying a fluorescence image in accordance with the present invention, the display means may be provided with the matrix operation circuit for transforming each of the light intensities into color signals and may be constituted such that a tint corresponding to each of the light intensities is capable of being selected arbitrarily by appropriately setting the coefficients of the operation formula in the matrix operation circuit. In such cases, the display color is capable of being adjusted so as to match with the sensitivity of the human eyes. Therefore, the person who sees the displayed fluorescence image is capable of recognizing with an enhanced reliability as to whether the fluorescence, which has been produced from the measuring site, is the fluorescence produced from the normal tissues or the fluorescence produced from the diseased tissues.